Surface Metal-Insulator Transition on a Vanadium Pentoxide (001) Single Crystal

In situ band gap mapping of the ${\mathrm{V}}_{2}{\mathrm{O}}_{5}(001)$ crystal surface revealed a reversible metal-to-insulator transition at 350--400 K, which occurs inhomogeneously across the surface and expands preferentially in the direction of the vanadyl ($\mathrm{V}=\mathrm{O}$) double rows. Supported by density functional theory and Monte Carlo simulations, the results are rationalized on the basis of the anisotropic growth of vanadyl-oxygen vacancies and a concomitant oxygen loss driven metal-to-insulator transition at the surface. At elevated temperatures irreversible surface reduction proceeds sequentially as ${\mathrm{V}}_{2}{\mathrm{O}}_{5}(001)\ensuremath{\rightarrow}{\mathrm{V}}_{6}{\mathrm{O}}_{13}(001)\ensuremath{\rightarrow}{\mathrm{V}}_{2}{\mathrm{O}}_{3}(0001)$.